When glass fibers are used in alkaline environments, such as when they are used as fibrous reinforcement for Portland cement, they are attacked by the alkali and deteriorate rapidly. Since economic and environmental considerations have made the use of glass fiber for cement reinforcement much more attractive in recent years, there have been numerous efforts to render glass fibers less susceptible to alkaline attack. These efforts have had two principal directions: First, much effort has been directed toward developing glass compositions which are themselves resistant to alkaline attack. For instance, one type of glass composition which is commercially used and considered moderately alkaline resistant contains large amounts of zirconia. Fibers made of such compositions deteriorate much less rapidly in alkaline environments than do fibers made of conventional glass compositions such as the well-known "E glass." The alkali resistant glass compositions, however, are quite expensive and thus cannot be readily used for such purposes as cement reinforcement without unduly raising the cost of the finished cement product.
The second approach to imparting alkali resistance to glass articles has been to develop coatings for the glass fibers which will prevent the alkaline components from contacting and attacking the glass surface. Use of such coatings is intended to allow the glass fiber to be composed of inexpensive and conventional materials such as those in the aforementioned "E glass." Alternatively, use of such coatings on fibers of alkali resistant glass compositions would enhance that alkali resistance and significantly extend the useful life of the expensive alkali resistant fibers, thus improving the economics of their use for cement reinforcement and similar uses.
Zinc stearate has been used for fiber coating in the past in minute quantities to impart a measure of moisture resistance to the fiber body. Such use is illustrated in U.S. Pat. Nos. 2,019,021; 2,022,750 and 2,728,949. It has also been used glass coatings in very small amounts to provide a degree of lubrication; see U.S. Pat. No. 3,025,588. Water soluble low molecular weight zinc compounds (specifically those which are salts of weak acids such as zinc formate, zinc acetate and zinc oxalate) have been used as surface coatings to impart a degree of alkali resistance to glass fiber; see U.S. Pat. No. 4,013,478. Film forming polymeric resins are widely used as a principal component in glass fiber sizes used to impart abrasion resistance or compatibility with organic resin bodies which the glass fibers are intended to reinforce. See, e.g., U.S. Pat. No. 4,147,555.
It is an object of this invention to provide a coating for glass fiber which will impart a significant degree of alkali resistance to the glass fiber and which can be readily applied and which is retained on the glass fiber in an alkaline, especially cement, environment. It is also an object of this invention to provide an alkali resistant coated glass fiber article.